Process for the recovery of copper compounds from the waste liquors of the cuprammonium silk stretch spinning process



Patented Aug. 1, 1933 STATES PROCESS THE RECQVERY OF COPPER CGM'PDUNDSFRQM THE WASTE LIQUORS OF THE CUPRAMREQNHJll I SILK STRETCH SPINNINGPROCESS m0 Mutti, Gozzano, Italy, assignor to The Firm American BembergCorporation, New York, N. Y., a Corporation of Delaware No Drawing.Application March 27,1931, Serial No. 525,862, and in Germany March 28,193d 17 Claims. (Cl. 23-125) It is already known in the production ofcuprammonium silk to remove the copper from the usually alkalineprecipitating. liquid by introduc-- ing carbohydrates, cellulose or woodmeal into the liquid. These substances have the property of absorbingcopper from the liquid. After the completion of the absorption thecopper precipitated by the substances is completely brought intosolution again by means of acid and may then be re-used.

It is also known to recover the copper from the precipitating liquidused in the, manufacture of cuprammonium silk by first of all expellingammonia by suitable expedients and then precipitating out the copper asan insoluble compound, usually as oxide or hydroxide.

These known processes, however, have not led to a satisfactory result inthe case of the precipitating liquid used in the production ofcuprammonium silk according to the stretch spinning process, since inthis process the copper occurs extraordinarily great dilution. Theabsorptive properties of the substances mentioned in the, introductionare no longer suflicient to remove copper from the solution withpractical completeness. Similarly, the employment of the second processis out of the question since the vaporization of the ammonia, in view ofthe small concentration, is not economical enough.

In the precipitating liquid which comes into question copper iscontained to the extent of approximately 0.01%, partially in the form ofhydroxide and partially in the form of basic sulphate, and it isdissolved in the liquid in a more or .less colloidal form. Organicsubstances, more particularly cellulose degradation products, here byact as protectivecolloids.

The present invention has for its object in the first place a recoveryof the copper from the highly diluted precipitating liquid which is ascomplete as possible. The invention further has for its object to employfor this purpose to the maximum possible extent the other waste liquorssuch as are formed during the preparation of the cotton for thecellulose solution and during the aoidi fication of the final spunfilament. Furthermore, according to the invention, the precipitatingliquid which has been freed from copper may be neutralized so that it isno longer injurious, for example, for the multiplying of fish. Finally,it is also possible, according to the invention, to use the auxiliarysubstance employed in a cyclic manner.

The invention consists in this that the copper containing precipitatingliquid is first of all ton 'as the alkaline acting solution.

reated with an excess of a solution of alkali, usually. soda lye. Inaddition a solution of magnesium salt is added so that magnesiumhydroxide is formed by reaction of the excess soda lye with themagnesium salt, which hydroxide carries down copper hydroxidepractically complete ly in the precipitating liquid, In this manner amud is formed comprised of copper hydroxide and magnesium hydroxidewhich readily settles on the bottom of the reaction vessel or may bepressed out iniilter presses.

It is advantageous to use the bucking lye which is obtained duringpreparation of the cot- It is true, lye contains a considerable quantityof cel' lulose degradation products, but these do not exert anyinjurious action during the precipitation, since themagnesium hydroxideproduced by double decomposition removes the undesirable colloidalproperties of these substances.

It is also advantageous if the quantity of magnesium salt added is soadjusted that it just corresponds to the excess of alkaline solutionadded, so that, e. g., a quantity of magnesium sulphate equivalent tothe excess of sodium hydroxide is added. In this manner the liquid freedfrom the mud contains merely sodium sulphate, which no longer injurious,so that the liquid may flow away without any further treatment.

The precipitate, which contains, besides organic impurities, hydroxideand magnesium hydroxide, is preferably worked up in such a way that itistreated with acid, particularly sulphuric acid, to such an extent thatthe magnesium hydroxide dissolves in the form of magnesium sulphate andthe copper hydroxide is converted wholly or partially into insolublebasic copper sulphate. For this purpose the copper-containing sulphuricacid which is obtained during the acidification of'the filaments, mayadvantageously be used, the copper sulphate in the said acid beingconverted during the treatment with the hydroxide-containing mud intoinsoluble basic copper sulphate.

By means or this reaction, therefore, a mud obtained consisting mainlyof basic copper sulphate and permeated merely with organic impz it-i-es,whilst on the other hand a solution of magnesium salt is formed. Thissolution may be reernployed without any further preliminary for theprecipitation of copper from the spent precipitating liquid. Theprocess, therefore, enables the magnesium salt used to be employed in acyclic manner. I

The precipitate obtained in this way, consistsubstantially only coppercellulose, may he remove-d lay cautious washing with cuprannnoniumsolution. The copper mud ohtainec in this manner may l aeused for addingto the cellulose solution again'either directly or after dissolution insulphuric acid and precipita tion with soda" copper sulphate. V

One modification of the invention is described by way of example in thefollowing:

In 5,008 cubic metres of precipitating liquid there are kg. of copper.To this quantityof precipitating liquid is added soda lye in an amountwhich corresponds to 1350 kg. of solid caustic soda. In addition 110%lag. of magnesium sulphate are added in order to neutralize the addedexcess 01": caustic soda, about 530 kg. of magnesium hydroxide beingformed thereby. In this manner a-mixture of copper hydroxide andmagnesium hydroxide is formed which contains 788 kg. ofcopper hydroxide.The mud formed solution in the formoi basic is separated ofi from thesupernatant liquid a suitable manner, 'e. gtby; filtration. To this vmxture is added spinning acid obtained during -e acidification oithefilaments in such quantity that practically not only all the magnesiumhydroxide is converted intoimagnesium sulphate, but th copper hydroxideof the mud and the copper sulphate contained in the nningiacid are alsocompletely converted into hasic copper sulphate.

.If it is assumed that the spinningacid con- 'tains 1% of copper and5.25% of free sulphuric acid, then 16.6 cubic metres of spinning acidare necessary for completelycarrying out this conversion. 1 If thespinning acid contains more sulphuric acid at the same copper content,then it is necessary to diminish theacid content to a correspondingextent by'addition of magnesium carbonate and the like.

The crude'basic copper sulphate obtained in this manner is filtered oil"and cautiously heated at about 40 C. in order to destroy the organicimpurities, whilst the magnesium sulphate 501w tion which also obtainedis reemployed for obtaining copper from the spent precipitating liquid.r r

The ignited basic copper sulphate maybe dissolved in acid once more forthe purpose of vfurther purification, spinning acid, for example,

' phate so obtained pure basic sulphate may be obtained in the knownmanner by precipitating with soda in the hot; this basic sulphate may beused'again for to the ccllulosesolution.

What I claim is: y l

l. A process for recovering copper compounds from highly diluted coppercontaining precipitating liquid obtained the cupranirnoniuni sill;stretch spin? .ng which comprises to the, liquid an alkali and asolution of 3;- am salt, the mu containing copper 0 do and niagnes "nwhich. ned being separated on fi'cin thesupernat liquid. '2. A processas claimed in claim 1, charac terized' by the feature that the buckinglye ohtained during the preparation of the cotton is used as thealkaline acting solution for the procipitation of the copper.

3. A process as claimed in claim 1, characteri ed by the feature that aquantity of magnes. in. salt is used for the precipitation which isequivalent to the excess of alkali.

4. A process as claimed in claim 1, characterized by the feature thatmagnesium sulphate is used for the precipitation.

5. A process as claimed in claim 1, characterized by the feature thatthe copper-containing mud obtained is treated with. a quantity of acid,such that the magnesium hydroxide of the mud dissolves up as magnesiumsalt, and the 1 copper hydroxide is wholly or partially converted tobasic-insoluble copper salt.

6.- A process as'claimed in claim 1, characterized'by the feature thatthe copper-containing sulphuric acid which is obtained during theacidification of the filaments is used for working up thecopper-containing mud in such a cuiantity that the copper sulphatecontained therein is also converted by the reaction into treatment ofthe mud containing copper and magnesium is freed from contaminatingcellulose degradation products by washing with. cuprammoniurn solution.

9. A process acclaimed in claim' 1, characterized by thefeature, thatthe contaminating cellulose degradation products are destroyed byignition in'an excess of air. a 1

10. A process as claimed in claim 1,'in which the copper-containing mudis treated with sulphuric .acid, whereby the magnesium hydroxide of themud isdissolved as magnesium salt, and the copper hydroxide is at leastin part converted to basic copper sulphate.

11. The process of recovering copper compounds irom a dilute solutioncontaining the same; which comprises. a step of precipitating magnesiumhydroxide in the solution.

-12. The process of recovering copper compounds froina dilute solutioncontaining the same, which comprises the steps of precipitating.magnesium hydroxide in the solution to carry treating the remainingmass with an acid ca.-

e of forming a soluhlemagnesium salt, and

an. insoluble copper salt.

1 A. process for recovering copper from a dilute solution containing thesame, which como A rises arr-ding an alkaline material. andprecipitating magnesium hydroxide in the solution,

separating out the precipitate, and adding sufiicient acid to dissolvethe magnesium and produce an insoluble salt of copper.

ill)

15. A process for recovering copper compounds from dilute solutionscontaining the same, which comprises adding an alkali and a solution ofa magnesium salt in such quantities as to precipitate magnesiumhydroxide in the solution.

16. A process as defined in claim 15in which

